1. Field of the Invention
The invention herein relates to compositions and methods for the formation of artificial human fingernail and toenail surfaces. More particularly, it relates to the formation of such surfaces using catalytic polymerization of cyanoacrylate monomers.
2. Description of the Prior Art
Artificial fingernail and toenail compositions in the form of nail coatings and extenders are well known and have become a major product line in the appearance and beauty industry. The appearance of one's fingernails (and in many cases also toenails) has become of importance to many fashion conscious individuals. The commercial artificial nail compositions have been used both for the purpose of enhancing the appearance of nails and also, in many cases, for enhancement of the physical properties of the nails, including providing strengthening to fragile nail surfaces.
It has been desirable to use cyanoacrylate polymers as part of artificial nail compositions. However, such has heretofore not been feasible in most cases, because of the problems with polymerizing (curing) cyanoacrylate monomers in the nail formation system.
The cyanoacrylate polymers are well known, especially for their adhesive properties. Their chemistry, methods of formation, compositions and uses are detailed widely; see, for example, Millet, "Cyanoacrylate Adhesives," Ch. 6, pp. 249-307, in Hartshorn, ed., Structural Adhesives: Chemistry and Technology (1986); Seymour, Engineering Polymer Sourcebook, Ch. 8, pp. 131-142 (1989); and Coover, "Cyanoacrylate Adhesives," Ch. 31, pp. 409-414, in Skeist, ed., Handbook of Adhesives (1962).
When used in the form of thin films, some cyanoacrylate monomers polymerize very rapidly in the presence of moisture. For these polymers, the amount of moisture in surrounding air is sufficient to cause complete polymerization of a thin film of the cyanoacrylate monomer, thus leading to the wide use of such cyanoacrylates as adhesives for bonding of tightly fitting surfaces.
However, many of these polymers, when in the form of thin films, lack flexibility, color stability or film strength. Other cyanoacrylate monomers polymerize only slowly in the presence of ambient moisture. In addition, many cyanoacrylate monomers (including those that otherwise would polymerize rapidly in the presence of ambient moisture) are initially mixed with inhibitors intended to prolong shelf life, which has the detrimental side effect that desirable polymerization speed is substantially slowed. There is thus a need for a catalyst that would speed the thin film polymerization of the normally slow cyanoacrylate monomers, overcome the retarding effects of inhibitors mixed with other cyanoacrylate monomers, and provide flexibility, color stability and/or strength to thin cyanoacrylate polymer films.
Moreover, in most nail formation systems, at least a portion of the cyanoacrylate monomer is present as a thicker layer (i.e., in "bulk"), and in such systems most cyanoacrylate monomers do not polymerize well. Polymerization in bulk is usually incomplete and the presence of unreacted monomer is detrimental to the properties of the polymerized product. It is believed that the polymerization of the bulk material is incomplete because the ambient moisture which catalyzes the thin film polymerization cannot penetrate satisfactorily into the body of the thicker layers of the cyanoacrylate monomer, and even that amount of moisture which does penetrate does not act effectively as a catalyst.
To this end there have been suggestions of a number of additive materials which could be incorporated into the cyanoacrylate monomer composition in an attempt to catalyze bulk polymerization fully. Some of the additives have been in the form of polymerization initiators but these are not usually satisfactory since they do not provide for shelf life prior to use. Another group of additives which has been suggested are promoters, which rely on separate initiation of polymerization by a third component. While such promoters can be blended with the cyanoacrylate monomers without causing any reaction, there is still the necessity of having a separate initiator before the polymerization promoters become effective.
While a number of the additives have been effective for completing or accelerating polymerization, they present problems, particularly in the area of safety, which can prevent their full utilization. As a first example of such problems, many of the catalytic reactions which result generate severe exotherms, which cause the polymerized cyanoacrylate material to become overheated. The presence of such excess heat can deteriorate the polymer bonds, discolor the polymerized body and detrimentally affect other additive materials which may be present in the composition or the surfaces with which the cyanoacrylate polymer is in contact. Thus, when cyanoacrylate polymers are used as a artificial nail compositions, the exothermic reaction which occurs can not only discolor the decorative nail surface but can often be of sufficient magnitude that the person's real nails and in some cases even the underlying tissue are seriously harmed by the heat. Of course even where there is no actual burning or blistering of the nails or tissue, the person usually experiences a great deal of discomfort from the heat.
It has also been found that many of the catalyst compositions are toxic, either when inhaled as fumes or when placed in contact with the human skin. Again considering nail compositions, a volatile toxic catalyst can be inhaled by both the wearer of the nail compositions and by the beautician or other person who applies the compositions. Both also can absorb the material through the skin, either by directly touching the composition while it is being applied to the wearer's nails or by absorption of fumes through the various skin surfaces which are in contact with the ambient air.
This is particularly significant when, as is commonly done, the compositions are sprayed onto the wearer's nails from a spray applicator held by the beautician at a distance of 6-12 inches (15-30 cm) from the nails. The spray creates a "mist cloud" which contacts the wearer's skin and the beautician's skin and is inhaled by both.
Finally, many of the proposed catalytic materials react only fairly slowly and do not provide quick polymerization of the slow or bulk cyanoacrylate monomers. This requires that such compositions must be set in place for some time before the cyanoacrylate monomer is fully polymerized. In many cases this is difficult or disadvantageous.
It would, therefore, be of great value to have a method and catalytic system which would allow for complete and rapid polymerization of cyanoacrylate monomers in the formation of artificial nail surfaces, so that the polymerization would be complete throughout the entire nail composition. Most importantly, such a method and system should also be safe for both the beautician to apply and the wearer to wear. Thus it would operate without the presence of any significant exotherm; would not cause harm to any adjoining material, whether human tissue or nails; would be satisfactory for use in either direct or indirect contact with people, of sufficiently low toxicity to be suitable for prolonged use by and in the presence of people and be acceptable for such human contact and use under the appropriate public health and cosmetics laws. Finally, it would not tend to discolor or distort the polymerized body; and the catalyst itself should be readily available,